Method and system for determining knock control fluid composition

ABSTRACT

Methods and systems are provided for accurately determining the composition of a knock control fluid using sensors already present in the engine system. An intake or an exhaust oxygen sensor is used to estimate the water and the alcohol content of a knock control fluid that is direct injected into an engine cylinder responsive to an indication of abnormal combustion. A change in the pumping current of the oxygen sensor due to the water content of the knock control fluid is distinguished from a change in the pumping current of the oxygen sensor due to the alcohol content of the knock control fluid.

FIELD

The present description relates generally to methods and systems fordetermining the composition of a wiper fluid injected into an engine forknock control.

BACKGROUND/SUMMARY

A variety of knock control fluids have been developed to mitigateabnormal combustion events, including various combinations of gasoline,ethanol, methanol, other alcohols, water, and other inert fluids. Waterinjection, for example, reduces knock, provides charge cooling, andreduces the octane requirement. In addition, since water injection canalso be used for engine dilution control, the need for a dedicated knockcontrol fluid is reduced.

Another example of a knock control fluid is shown by Surnilla in U.S.Pat. No. 7,533,651. Therein, direct injection of a washer fluid, whichincludes water and alcohol (e.g., engine coolant or methanol) leveragesthe charge cooling properties of the both the fluid and the directinjection to reduce knock. In addition to protecting the water fromfreezing, the inclusion of engine coolant in the composition of theinjected knock control fluid offers an added advantage of having lighthydrocarbons (such as methanol), which help in the combustion process.The overall approach increases engine efficiency while reducing theoctane requirement of injected fuel, thereby increasing the power outputof the engine. Herein, the wiper fluid can be repurposed for knockcontrol in addition to being used for cleaning a vehicle windshield.

However, the inventors herein have recognized an issue with theapproach. There may be variations in windshield wiper fluid composition.For example, there may be a wide variation in the ethanol or methanolcontent of the fluid, as such. In addition, when a windshield wiperfluid tank is refilled, based on an amount and composition of wiperfluid that was left over in the tank, the composition of the availablewiper fluid following the refilling may vary. While this does not affectthe fluid's ability to clean a windshield wiper, it may affect the knockcontrolling ability of the fluid. For example, the octane value of thefluid may change. As such, various engine parameters are adjusted basedon the injected knock control fluid. For example, based on the alcoholcontent of the injected fluid, cylinder fueling may be adjusted. Inaddition, engine parameters may need to be adjusted based on the type ofalcohol in the fluid (e.g., whether the alcohol is ethanol or methanol).As a result, errors in the estimation of a wiper fluid composition canresult in significant air-fuel errors, degrading engine performance.Further, if the composition of a wiper fluid is not accurately known,use of wiper fluid as a knock control fluid may be limited. On the otherhand, the addition of a sensor dedicated to estimating the alcoholcontent and composition of a knock control fluid may add significantcost and complexity.

In one example, the issues described above may be addressed by a methodfor an engine comprising: during selected conditions, injecting anamount of a water-alcohol blend into an engine intake; applying avoltage to an intake oxygen sensor; monitoring a change in pumpingcurrent of the sensor; learning a first portion of the change in pumpingcurrent due to a water content of the blend; and learning a secondportion of the change in pumping current due to an alcohol content ofthe blend. In this way, the composition of a knock control fluidinjected into an engine can be accurately determined using existingengine sensors.

As an example, following refilling of a wiper fluid tank, a wiper fluidcomposition may be estimated using an intake oxygen sensor. The wiperfluid may then be used as a knock control fluid. As such, the wiperfluid may include a mixture of water and alcohol but no gasoline.Further, an alcohol type in the fluid may be known a priori. Forexample, it may be known that the wiper fluid is a water-ethanolmixture, or a water-methanol mixture. However, a ratio of water to thespecified alcohol in the fluid may not be accurately known. A controllermay inject a defined mass of the knock control fluid into the engineintake, such as into the intake manifold, downstream of an intakethrottle and upstream of an intake oxygen sensor. The fluid may beinjected while EGR is disabled to reduce interference on the resultsfrom EGR. A lower reference voltage (e.g., 450 mV) may then be appliedto the intake oxygen sensor and an output of the sensor may be noted.For example, a pumping current (or change in pumping current) may beoutput. As such, the pumping current may be affected by a reduction inthe oxygen concentration at the oxygen sensor due to the water contentof the knock control fluid as well as due to the alcohol content of theknock control fluid. Specifically, the water in the knock control fluidmay have a dilution effect on the oxygen sensor while the alcohol in theknock control fluid may combust with oxygen at the sensor, reducing theoxygen concentration at the sensor. An engine controller may thencalculate the alcohol content of the knock control fluid based on achange in the pumping current, as well as the injection mass. Forexample, the engine controller may reference a 3D calibration map toestimate the alcohol content of the fluid, and update the composition ofthe fluid. By learning the composition of the fluid, the flexibility ofusage of the wiper fluid as a knock control fluid may be enhanced.

In this way, an intake oxygen sensor can be used to estimate thecomposition (including the hydrocarbon type and alcohol content) of aknock control fluid. The technical effect of modulating the referencevoltage of an intake oxygen sensor is that a change in the pumpingcurrent of the sensor that is attributed to the water component of theknock control fluid can be better distinguished from the changeattributed to the alcohol component of the knock control fluid. This isdue to the fact that the dilution effect on the oxygen sensor has aremarkably different contribution than the combustion effect of thealcohol. By better estimating the composition of an injected knockcontrol fluid, the use of the knock control fluid may be expanded toengines of different fuel types, improving the robustness of the system.In addition, the accuracy of fuel octane estimates may be increased,which allows spark control to be improved. For example, spark retardusage for knock control may be reduced providing fuel economy benefits.By using an existing intake oxygen sensor to determine the compositionof the knock control fluid, the need for a dedicated sensor is reducedwithout compromising on the accuracy of the estimation.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine system.

FIG. 2 shows a detailed diagram of an engine combustion chamber.

FIG. 3 shows a schematic diagram of an example oxygen sensor.

FIG. 4 shows a flow chart illustrating a routine for using an intakeoxygen sensor for knock control fluid alcohol estimation.

FIG. 5 shows a flow chart illustrating a routine for using an exhaustoxygen sensor for knock control fluid alcohol estimation.

FIG. 6 shows a map demonstrating an example relationship between analcohol content of a knock control fluid relative and each of a changein the pumping current of an oxygen sensor, and a mass of the knockcontrol fluid injected into an engine.

DETAILED DESCRIPTION

The following description relates to systems and methods for determiningthe composition of a knock control fluid injected into an engine, suchas the engine of FIGS. 1-2, based on outputs from an intake oxygensensor, such as the sensor of FIG. 3. As such, the intake oxygen sensormay be used during different engine operating conditions to estimate thealcohol content of a fuel delivered to the engine during enginecombustion, or the alcohol composition of the knock control fluiddelivered to the engine responsive to an indication of knock (FIG. 3).An engine controller may be configured to perform a control routine,such as the example routine of FIGS. 4-5, to estimate the composition ofthe knock control fluid, including the alcohol content and thehydrocarbon content of the fluid, based on a change in the pumpingcurrent of the intake oxygen sensor upon modulation of a referencevoltage. The controller may reference a map, such as the example map ofFIG. 6, to correlate the change in pumping current and the injectionmass with the alcohol content of the injected fluid. One or more engineoperating parameters such as spark timing and/or fuel injection amountmay be adjusted based on the determined composition of the knock controlfluid. In this manner, engine knock control fluid usage may be expanded.

FIG. 1 shows a schematic depiction of an example turbocharged enginesystem 100 including a multi-cylinder internal combustion engine 10 andtwin turbochargers 120 and 130. As one non-limiting example, enginesystem 100 can be included as part of a propulsion system for apassenger vehicle. Engine system 100 can receive intake air via intakepassage 140. Intake passage 140 can include an air filter 156 and an EGRthrottle valve 131. Engine system 100 may be a split-engine systemwherein intake passage 140 is branched downstream of EGR throttle valve131 into first and second parallel intake passages, each including aturbocharger compressor. Specifically, at least a portion of intake airis directed to compressor 122 of turbocharger 120 via a first parallelintake passage 142 and at least another portion of the intake air isdirected to compressor 132 of turbocharger 130 via a second parallelintake passage 144 of the intake passage 140.

The first portion of the total intake air that is compressed bycompressor 122 may be supplied to intake manifold 160 via first parallelbranched intake passage 146. In this way, intake passages 142 and 146form a first parallel branch of the engine's air intake system.Similarly, a second portion of the total intake air can be compressedvia compressor 132 where it may be supplied to intake manifold 160 viasecond parallel branched intake passage 148. Thus, intake passages 144and 148 form a second parallel branch of the engine's air intake system.As shown in FIG. 1, intake air from intake passages 146 and 148 can berecombined via a common intake passage 149 before reaching intakemanifold 160, where the intake air may be provided to the engine.

A first EGR throttle valve 131 may be positioned in the engine intakeupstream of the first and second parallel intake passages 142 and 144,while a second air intake throttle valve 158 may be positioned in theengine intake downstream of the first and second parallel intakepassages 142 and 144, and downstream of the first and second parallelbranched intake passages 146 and 148, for example, in common intakepassage 149.

In some examples, intake manifold 160 may include an intake manifoldpressure sensor 182 for estimating a manifold pressure (MAP) and/or anintake manifold temperature sensor 183 for estimating a manifold airtemperature (MCT), each communicating with controller 12. Intake passage149 can include a charge air cooler (CAC) 154 and/or a throttle (such assecond throttle valve 158). The position of throttle valve 158 can beadjusted by the control system via a throttle actuator (not shown)communicatively coupled to controller 12. An anti-surge valve 152 may beprovided to selectively bypass the compressor stages of turbochargers120 and 130 via bypass passage 150. As one example, anti-surge valve 152can open to enable flow through bypass passage 150 when the intake airpressure upstream of the compressors attains a threshold value.

Intake manifold 160 may further include an intake gas oxygen sensor 172.In one example, the oxygen sensor is a UEGO sensor, such as the exampleUEGO sensor of FIG. 3. As elaborated herein, the intake gas oxygensensor may be configured to provide an estimate regarding the oxygencontent of fresh air received in the intake manifold. In addition, whenEGR is flowing, a change in oxygen concentration at the sensor may beused to infer an EGR amount and used for accurate EGR flow control.Further still, during selected fueling conditions, the reference voltageof the sensor may be modulated and the corresponding change in currentmay be used to infer the alcohol content of an injected fuel. As alsoelaborated herein, during conditions when a knock control fluid isinjected, the reference voltage of the sensor may be modulated and thecorresponding change in current may be used to infer and distinguish thewater content of the injected fluid from the alcohol content of theinjected fluid. In the depicted example, oxygen sensor 162 is positionedupstream of throttle 158 and downstream of charge air cooler 154.However, in alternate embodiments, the oxygen sensor may be positionedupstream of the CAC.

A pressure sensor 174 may be positioned alongside the oxygen sensor forestimating an intake pressure at which an output of the oxygen sensor isreceived. Since the output of the oxygen sensor is influenced by theintake pressure, a reference oxygen sensor output may be learned at areference intake pressure. In one example, the reference intake pressureis a throttle inlet pressure (TIP) where pressure sensor 174 is a TIPsensor. In alternate examples, the reference intake pressure is amanifold pressure (MAP) as sensed by MAP sensor 182.

Engine 10 may include a plurality of cylinders 14. In the depictedexample, engine 10 includes six cylinders arrange in a V-configuration.Specifically, the six cylinders are arranged on two banks 13 and 15,with each bank including three cylinders. In alternate examples, engine10 can include two or more cylinders such as 3, 4, 5, 8, 10 or morecylinders. These various cylinders can be equally divided and arrangedin alternate configurations, such as V, in-line, boxed, etc. Eachcylinder 14 may be configured with a fuel injector 166. In the depictedexample, fuel injector 166 is a direct in-cylinder injector. However, inother examples, fuel injector 166 can be configured as a port based fuelinjector.

Intake air supplied to each cylinder 14 (herein, also referred to ascombustion chamber 14) via common intake passage 149 may be used forfuel combustion and products of combustion may then be exhausted fromvia bank-specific parallel exhaust passages. In the depicted example, afirst bank 13 of cylinders of engine 10 can exhaust products ofcombustion via a first parallel exhaust passage 17 and a second bank 15of cylinders can exhaust products of combustion via a second parallelexhaust passage 19. Each of the first and second parallel exhaustpassages 17 and 19 may further include a turbocharger turbine.Specifically, products of combustion that are exhausted via exhaustpassage 17 can be directed through exhaust turbine 124 of turbocharger120, which in turn can provide mechanical work to compressor 122 viashaft 126 in order to provide compression to the intake air.Alternatively, some or all of the exhaust gases flowing through exhaustpassage 17 can bypass turbine 124 via turbine bypass passage 123 ascontrolled by wastegate 128. Similarly, products of combustion that areexhausted via exhaust passage 19 can be directed through exhaust turbine134 of turbocharger 130, which in turn can provide mechanical work tocompressor 132 via shaft 136 in order to provide compression to intakeair flowing through the second branch of the engine's intake system.Alternatively, some or all of the exhaust gas flowing through exhaustpassage 19 can bypass turbine 134 via turbine bypass passage 133 ascontrolled by wastegate 138.

In some examples, exhaust turbines 124 and 134 may be configured asvariable geometry turbines, wherein controller 12 may adjust theposition of the turbine impeller blades (or vanes) to vary the level ofenergy that is obtained from the exhaust gas flow and imparted to theirrespective compressor. Alternatively, exhaust turbines 124 and 134 maybe configured as variable nozzle turbines, wherein controller 12 mayadjust the position of the turbine nozzle to vary the level of energythat is obtained from the exhaust gas flow and imparted to theirrespective compressor. For example, the control system can be configuredto independently vary the vane or nozzle position of the exhaust gasturbines 124 and 134 via respective actuators.

Exhaust gases in first parallel exhaust passage 17 may be directed tothe atmosphere via branched parallel exhaust passage 170 while exhaustgases in second parallel exhaust passage 19 may be directed to theatmosphere via branched parallel exhaust passage 180. Exhaust passages170 and 180 may include one or more exhaust after-treatment devices,such as a catalyst, and one or more exhaust gas sensors.

Engine 10 may further include one or more exhaust gas recirculation(EGR) passages, or loops, for recirculating at least a portion ofexhaust gas from the exhaust manifold to the intake manifold. These mayinclude high-pressure EGR loops for proving high-pressure EGR (HP-EGR)and low-pressure EGR-loops for providing low-pressure EGR (LP-EGR). Inone example, HP-EGR may be provided in the absence of boost provided byturbochargers 120, 130, while LP-EGR may be provided in the presence ofturbocharger boost and/or when exhaust gas temperature is above athreshold. In still other examples, both HP-EGR and LP-EGR may beprovided simultaneously.

In the depicted example, engine 10 may include a low-pressure EGR loop202 for recirculating at least some exhaust gas from the first branchedparallel exhaust passage 170, downstream of the turbine 124, to thefirst parallel intake passage 142, upstream of the compressor 122. Insome embodiments, a second low-pressure EGR loop (not shown) may belikewise provided for recirculating at least some exhaust gas from thesecond branched parallel exhaust passage 180, downstream of the turbine134, to the second parallel intake passage 144, upstream of thecompressor 132. LP-EGR loop 202 may include LP-EGR valve 204 forcontrolling an EGR flow (i.e., an amount of exhaust gas recirculated)through the loops, as well as an EGR cooler 206 for lowering atemperature of exhaust gas flowing through the EGR loop beforerecirculation into the engine intake. Under certain conditions, the EGRcooler 206 may also be used to heat the exhaust gas flowing throughLP-EGR loop 202 before the exhaust gas enters the compressor to avoidwater droplets impinging on the compressors.

Engine 10 may further include a first high-pressure EGR loop 208 forrecirculating at least some exhaust gas from the first parallel exhaustpassage 17, upstream of the turbine 124, to intake manifold 160,downstream of intake throttle 158. Likewise, the engine may include asecond high-pressure EGR loop (not shown) for recirculating at leastsome exhaust gas from the second parallel exhaust passage 18, upstreamof the turbine 134, to the second branched parallel intake passage 148,downstream of the compressor 132. EGR flow through HP-EGR loops 208 maybe controlled via HP-EGR valve 210.

A PCV port 102 may be configured to deliver crankcase ventilation gases(blow-by gases) to the engine intake manifold along second parallelintake passage 144. In some embodiments, flow of PCV air through PCVport 102 may be controlled by a dedicated PCV port valve. Thus, when thePCV valve is closed, crankcase ventilation to the engine intake isdisabled. Likewise, a purge port 104 may be configured to deliver purgegases from a fuel system canister to the engine intake manifold alongpassage 144. In some embodiments, flow of purge air through purge port104 may be controlled by a dedicated purge port valve. Thus, when thepurge valve is closed, fuel vapor purging to the engine intake isdisabled

Humidity sensor 112 and pressure sensor 114 may be included in only oneof the parallel intake passages (herein, depicted in the first parallelintake air passage 142 but not in the second parallel intake passage144), downstream of EGR throttle valve 131. Specifically, the humiditysensor and the pressure sensor may be included in the intake passage notreceiving the PCV or purge air. Humidity sensor 112 may be configured toestimate a relative humidity of the intake air. In one embodiment,humidity sensor 112 is an oxygen sensor configured to estimate therelative humidity of the intake air based on the output of the sensor atone or more voltages. Since purge air and PCV air can confound theresults of the humidity sensor, the purge port and PCV port arepositioned in a distinct intake passage from the humidity sensor.Pressure sensor 114 may be configured to estimate a pressure of theintake air. In some embodiments, a temperature sensor may also beincluded in the same parallel intake passage, downstream of the EGRthrottle valve 131.

Intake oxygen sensor 172 may be used, during selected conditions, forestimating an intake oxygen concentration and inferring an amount of EGRdilution at the engine based on a change in the intake oxygenconcentration upon opening of the EGR valve 204. For example, uponapplying a reference voltage (Vs) to the sensor, a pumping current (Ip)is output by the sensor. The change in oxygen concentration may beproportional to the change in pumping current (delta Ip) output by thesensor. Likewise, during other selected conditions, intake oxygen sensor172 may be used for estimating the water content of intake charge (thatis, ambient humidity) or the water content of an injected fuel (andinferring the alcohol content of the injected fuel). Further still, aselaborated herein, during other conditions, the intake oxygen sensor maybe used for estimating the water content and alcohol content of a knockcontrol fluid and estimating a composition of the knock control fluidaccordingly. In one example, the knock control fluid is a wiper fluid.The reference voltage (Vs) may be applied to the sensor and a change inpumping current (Ip) output by the sensor may be learned. A firstportion of the change in pumping current (delta Ip) output by the sensorthat is due to the water content of the injected knock control fluid maybe learned, and distinguished from a second portion of the change inpumping current that is due to the alcohol content of the injected knockcontrol fluid.

In still other examples, an exhaust gas oxygen sensor, such as sensor248 of FIG. 2 may be used, during selected conditions, for estimatingone or more of the water content of an injected fuel (and inferring thealcohol content of the injected fuel), a ratio of the water contentrelative to alcohol content of a knock control fluid. Estimating acomposition of the knock control fluid may include modulating thereference voltage applied to the sensor between a higher and a lowervoltage, and learning a change in pumping current (Ip) output by thesensor. A first portion of the change in pumping current (delta Ip)output by the sensor that is due to the water content of the injectedknock control fluid may be learned, and distinguished from a secondportion of the change in pumping current that is due to the alcoholcontent of the injected knock control fluid.

The position of intake and exhaust valves of each cylinder 14 may beregulated via hydraulically actuated lifters coupled to valve pushrods,or via a direct acting mechanical bucket system in which cam lobes areused. In this example, at least the intake valves of each cylinder 14may be controlled by cam actuation using a cam actuation system.Specifically, the intake valve cam actuation system 25 may include oneor more cams and may utilize variable cam timing or lift for intakeand/or exhaust valves. In alternative embodiments, the intake valves maybe controlled by electric valve actuation. Similarly, the exhaust valvesmay be controlled by cam actuation systems or electric valve actuation.

Engine system 100 may be controlled at least partially by a controlsystem 15 including controller 12 and by input from a vehicle operatorvia an input device (not shown). Control system 15 is shown receivinginformation from a plurality of sensors 16 (various examples of whichare described herein at FIG. 1 and FIG. 2) and sending control signalsto a plurality of actuators 81. As one example, sensors 16 may includehumidity sensor 112, intake air pressure sensor 114, MAP sensor 182, MCTsensor 183, TIP sensor 174, and intake air oxygen sensor 172. In someexamples, common intake passage 149 may further include a throttle inlettemperature sensor for estimating a throttle air temperature (TCT). Inother examples, one or more of the EGR passages may include pressure,temperature, and air-to-fuel ratio sensors, for determining EGR flowcharacteristics. As another example, actuators 81 may include fuelinjector 166, HP-EGR valves 210 and 220, LP-EGR valves 204 and 214,throttle valves 158 and 131, and wastegates 128, 138. Other actuators,such as a variety of additional valves and throttles, may be coupled tovarious locations in engine system 100, such as those described withreference to FIG. 2. The controller 12 receives signals from the varioussensors of FIG. 1 (and FIG. 2) and employs the various actuators of FIG.1 (and FIG. 2) to adjust engine operation based on the received signalsand instructions stored on a memory of the controller. For example,controller 12 may receive input data from the various sensors, processthe input data, and trigger the actuators in response to the processedinput data based on instruction or code programmed therein correspondingto one or more routines. Example control routines are described hereinwith regard to FIGS. 4-5.

FIG. 2 depicts a detailed embodiment of a combustion chamber, such as acombustion chamber of engine 10 of FIG. 1. Components previouslyintroduced in FIG. 1 are numbered similarly and not reintroduced.

Engine 10 may receive control parameters from a control system includingcontroller 12 and input from a vehicle operator 230 via an input device232. In this example, input device 232 includes an accelerator pedal anda pedal position sensor 234 for generating a proportional pedal positionsignal PP. Cylinder (herein also “combustion chamber’) 14 of engine 10may include combustion chamber walls 236 with piston 238 positionedtherein. Piston 238 may be coupled to crankshaft 240 so thatreciprocating motion of the piston is translated into rotational motionof the crankshaft. Crankshaft 240 may be coupled to at least one drivewheel of the passenger vehicle via a transmission system. Further, astarter motor may be coupled to crankshaft 240 via a flywheel to enablea starting operation of engine 10.

Engine 10 is coupled in a vehicle system 100 that includes a windshieldwiper system that enables cleaning of a vehicle windshield 68.Windshield 68 may be a front or rear windshield of a vehicle. Thewindshield wiper system includes at least one windshield wiper 70operated by wiper motor 72. In response to an operator demand, and basedon input from controller 12, wiper motor 72 may be energized causingwiper 70 to make multiple sweeping cycles known as wipes or sweeps overwindshield 68. The wipes or sweeps enable wiper blade 71 to removemoisture, debris, and foreign particles from the surface of windshield68. While operating wiper motor 72 and while wiper blade 71 is sweeping,based on request from a vehicle operator, controller 12 mayintermittently inject or squirt a wiper fluid onto the windshield viawiper injector 74. Wiper fluid may be stored in a reservoir 76 fromwhere it is delivered to the windshield. As elaborated herein, reservoir76 may be further coupled to the intake passage as well as the enginecylinder. This allows the wiper fluid to be injected to provide knockcontrol in addition to being used for windshield wiping purposes.Specifically, the wiper fluid may be injected into the intake manifold,specifically into intake passage 246, downstream of the intake throttle,during knock conditions, thereby enabling the windshield wiper fluid tobe used as a knock control fluid. Additionally, or alternatively,windshield wiper fluid may be directed injected into an engine cylindervia direct injector, such as via the direct fuel injector or a dedicateddirect fuel injector, to provide knock control. The wiper fluid storedin reservoir 76 may include a combination of water and alcohol, such asmethanol or isopropanol. However, the wiper fluid does not contain anygasoline.

As such, there may be significant variation in the water:alcohol contentof the wiper fluid. To enable the wiper fluid to be reliably used as aknock control fluid, a composition of the wiper fluid may need to beknown. As elaborated with reference to FIG. 1, during selectedconditions, such as immediately after the wiper fluid reservoir has beenrefilled, an intake oxygen sensor, such as sensor 172, may be used toestimate the water to alcohol content of the wiper fluid. Alternatively,an exhaust gas oxygen sensor, such as sensor 228, may be used toestimate the water to alcohol content of the wiper fluid. Examplemethods for estimating a wiper fluid composition using an intake orexhaust oxygen sensor is shown with reference to FIGS. 4-5.

Cylinder 14 can receive intake air via a series of intake air passages242, 244, and 246. Intake air passage 246 may communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 2 shows engine 10configured with a turbocharger including a compressor 274 arrangedbetween intake passages 242 and 244, and an exhaust turbine 276 arrangedalong exhaust passage 248. Compressor 274 may be at least partiallypowered by exhaust turbine 276 via a shaft 280 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 276 maybe optionally omitted, where compressor 274 may be powered by mechanicalinput from a motor or the engine. A throttle 262 including a throttleplate 264 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 262 may be disposed downstreamof compressor 274 as shown in FIG. 2, or alternatively may be providedupstream of compressor 274.

Exhaust passage 248 may receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 228 is showncoupled to exhaust passage 248 upstream of emission control device 278.Sensor 228 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 278 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be measured by one or more temperature sensors(not shown) located in exhaust passage 248. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 228. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 250 and at least one exhaust poppet valve256 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 250 may be controlled by controller 12 by cam actuation viacam actuation system 251. Similarly, exhaust valve 256 may be controlledby controller 12 via cam actuation system 253. Cam actuation systems 251and 253 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The operation ofintake valve 250 and exhaust valve 256 may be determined by valveposition sensors (not shown) and/or camshaft position sensors 255 and257, respectively. In alternative embodiments, the intake and/or exhaustvalve may be controlled by electric valve actuation. For example,cylinder 14 may alternatively include an intake valve controlled viaelectric valve actuation and an exhaust valve controlled via camactuation including CPS and/or VCT systems. In still other embodiments,the intake and exhaust valves may be controlled by a common valveactuator or actuation system, or a variable valve timing actuator oractuation system.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 238 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug292 for initiating combustion. Ignition system 290 can provide anignition spark to combustion chamber 14 via spark plug 292 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 292 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more injectors for providing a knock control fluid thereto. Insome embodiments, the knock control fluid may be a fuel, wherein theinjector is also referred to as a fuel injector. As a non-limitingexample, cylinder 14 is shown including one fuel injector 266. Fuelinjector 266 is shown coupled directly to cylinder 14 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 268. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows injector 266 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 292. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 266 from a high pressure fuel system 8 including one ormore fuel tanks 78, fuel pumps, and a fuel rail. Alternatively, fuel maybe delivered by a single stage fuel pump at lower pressure, in whichcase the timing of the direct fuel injection may be more limited duringthe compression stroke than if a high pressure fuel system is used.Further, while not shown, fuel tanks 78 may have a pressure transducerproviding a signal to controller 12. It will be appreciated that, in analternate embodiment, injector 266 may be a port injector providing fuelinto the intake port upstream of cylinder 14.

Fuel may be delivered by the injector to the cylinder during a singlecycle of the cylinder. Further, the distribution and/or relative amountof fuel delivered from the injector may vary with operating conditions,such as aircharge temperature, as described herein below. Furthermore,for a single combustion event, multiple injections of the delivered fuelmay be performed per cycle. The multiple injections may be performedduring the compression stroke, intake stroke, or any appropriatecombination thereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks 78 in fuel system 8 may hold fuel or knock control fluidswith different qualities, such as different compositions. Thesedifferences may include different alcohol content, different watercontent, different octane, different heat of vaporizations, differentfuel blends, different water contents, different flammability limits,and/or combinations thereof etc. In one example, knock control fluidswith different alcohol contents could include one fuel being gasolineand the other being ethanol or methanol. Other alcohol containing fuelscould be a mixture of alcohol and water, a mixture of alcohol, water,etc. In still another example, both fuels may be alcohol blends whereinthe first fuel may be a gasoline alcohol blend with a lower ratio ofalcohol than a gasoline alcohol blend of a second fuel with a greaterratio of alcohol, such as E10 (which is approximately 10% ethanol) as afirst fuel and E85 (which is approximately 85% ethanol) as a secondfuel. Additionally, the first and second fuels may also differ in otherfuel qualities such as a difference in temperature, viscosity, octanenumber, latent enthalpy of vaporization etc.

Moreover, fuel characteristics of the fuel or knock control fluid storedin the fuel tank may vary frequently. The day to day variations in tankrefilling can thus result in frequently varying fuel compositions,thereby affecting the fuel composition delivered by injector 166.

In addition to the fuel tanks, fuel system 8 may also include areservoir 76 for storing a knock control fluid, herein windshield wiperfluid. While reservoir 76 is depicted as being distinct from the one ormore fuel tanks 78, it will be appreciated that in alternate examples,reservoir 76 may be one of the one of more fuel tanks 78. Reservoir 76may be coupled to direct injector 266 so that wiper fluid can bedirectly injected into cylinder 14. During some conditions, in responseto an indication of knock, an engine controller may inject wiper fluid,being using as a knock control fluid, into the intake manifold,downstream of the intake throttle, to increase engine dilution andthereby control the untimely and unwanted detonation event.Alternatively, or additionally, in response to an indication of knock,the engine controller may directly inject wiper fluid, being using as aknock control fluid, into the engine cylinder to increase enginedilution and thereby control the untimely and unwanted detonation event

In some embodiments, the fuel system may also include a reservoir forstoring water that is coupled to the direct injector so that water maybe direct injected into the cylinder. As such, by injecting water,“liquid EGR” is provided, which enables substantial EGR benefits to beachieved. However, during conditions when liquid needs to be conserved,or when a back-up is required for when liquid EGR is not present,external EGR system may be added.

The engine may further include one or more exhaust gas recirculationpassages for diverting at least a portion of exhaust gas from the engineexhaust to the engine intake. FIG. 2 shows a low pressure EGR (LP-EGR)system, but an alternative embodiment may include only a high pressureEGR (HP-EGR) system, or a combination of both LP-EGR and HP-EGR systems.The LP-EGR is routed through LP-EGR passage 249 from downstream ofturbine 276 to upstream of compressor 274. The amount of LP-EGR providedto intake manifold 244 may be varied by controller 12 via LP-EGR valve252. The LP-EGR system may include LP-EGR cooler 258 to reject heat fromthe EGR gases to engine coolant, for example. When included, the HP-EGRsystem may route HP-EGR through a dedicated HP-EGR passage (not shown)from upstream of turbine 276 to downstream of compressor 274 (andupstream of intake throttle 262), via an HP-EGR cooler. The amount ofHP-EGR provided to intake manifold 244 may be varied by controller 12via an HP-EGR valve (not shown).

Under some conditions, the EGR system may be used to regulate thetemperature of the air and fuel mixture within combustion chamber 14.Thus, it may be desirable to measure or estimate the EGR mass flow. Forexample, one or more sensors 259 may be positioned within LP-EGR passage249 to provide an indication of one or more of a pressure, temperature,and air-fuel ratio of exhaust gas recirculated through the LP-EGRpassage. Exhaust gas diverted through LP-EGR passage 249 may be dilutedwith fresh intake air at a mixing point located at the junction ofLP-EGR passage 249 and intake passage 242. In some examples, where anair intake system (AIS) throttle is included in intake passage 242,upstream of compressor 274, by adjusting LP-EGR valve 252 incoordination with the air intake system throttle, a dilution of the EGRflow may be adjusted.

A percent dilution of the LP-EGR flow may be inferred from the output ofa sensor in the engine intake gas stream. For example, a sensor 172positioned downstream of LP-EGR valve 252, and upstream of main intakethrottle 262, may be used so that the LP-EGR dilution at or close to themain intake throttle may be accurately determined. Sensor 172 may be,for example, an oxygen sensor. In addition, during selected conditions,sensor 172 may be used for estimating the alcohol content of fueldelivered to the engine, as well as the alcohol content and compositionof a knock control fluid delivered to cylinder 14.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 206, input/output ports 208, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 210 in this particular example, random access memory 212,keep alive memory 214, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 222; engine coolant temperature (ECT)from temperature sensor 216 coupled to cooling sleeve 218; a profileignition pickup signal (PIP) from Hall effect sensor 220 (or other type)coupled to crankshaft 240; throttle position (TP) from a throttleposition sensor; and manifold absolute pressure signal (MAP) from sensor224. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Still other sensors may include fuel level sensors andfuel composition sensors coupled to the fuel tank(s) of the fuel system.Controller 12 may also receive an operator request for windshield wipingvia a dedicated sensor (not shown). In response to the signals receivedfrom the various sensors, the controller may operate various engineactuators. Example actuators include fuel injector 266, wiper motor 72,wiper injector 74, throttle 262, cams 251 and 253, etc. Storage mediumread-only memory 210 can be programmed with computer readable datarepresenting instructions executable by processor 206 for performing themethods described below as well as other variants that are anticipatedbut not specifically listed. Example routines that may be performed areelaborated with reference to FIGS. 4-5.

Next, FIG. 3 shows a schematic view of an example embodiment of anoxygen sensor 300 configured to measure a concentration of oxygen (O₂)in an intake aircharge stream. Sensor 300 may operate as intake oxygensensor 172 of FIGS. 1-2, or exhaust gas oxygen sensor 226 of FIGS. 1-2,for example. Sensor 300 comprises a plurality of layers of one or moreceramic materials arranged in a stacked configuration. In the embodimentof FIG. 3, five ceramic layers are depicted as layers 301, 302, 303,304, and 305. These layers include one or more layers of a solidelectrolyte capable of conducting ionic oxygen. Examples of suitablesolid electrolytes include, but are not limited to, zirconiumoxide-based materials. Further, in some embodiments, a heater 307 may bedisposed in thermal communication with the layers to increase the ionicconductivity of the layers. While the depicted oxygen sensor is formedfrom five ceramic layers, it will be appreciated that the oxygen sensormay include other suitable numbers of ceramic layers.

Layer 302 includes a material or materials creating a diffusion path310. Diffusion path 310 is configured to introduce intake gases into afirst internal cavity 322 via diffusion. Diffusion path 310 may beconfigured to allow one or more components of exhaust gases, includingbut not limited to a desired analyte (e.g., O₂), to diffuse intointernal cavity 322 at a more limiting rate than the analyte can bepumped in or out by pumping electrodes pair 312 and 314. In this manner,a stoichiometric level of O₂ may be obtained in the first internalcavity 322. Sensor 300 further includes a second internal cavity 324within layer 304 separated from the first internal cavity 322 by layer303. The second internal cavity 324 is configured to maintain a constantoxygen partial pressure equivalent to a stoichiometric condition, e.g.,an oxygen level present in the second internal cavity 324 is equal tothat which the exhaust gas would have if the air-fuel ratio wasstoichiometric. Herein, second internal cavity 324 may be referred to asa reference cell. As shown, the reference voltage is variable (e.g.,between 0 and 1300 mV).

A pair of sensing electrodes 316 and 318 is disposed in communicationwith first internal cavity 322 and reference cell 324. The sensingelectrodes pair 316 and 318 detects a concentration gradient that maydevelop between the first internal cavity 322 and the reference cell 324due to an oxygen concentration in the intake air that is higher than orlower than the stoichiometric level. A high oxygen concentration may becaused by a lean charge mixture, while a low oxygen concentration may becaused by a rich charge mixture.

A pair of pumping electrodes 312 and 314 is disposed in communicationwith internal cavity 322, and is configured to electrochemically pump aselected gas constituent (e.g., O₂) from internal cavity 322 throughlayer 301 and out of sensor 300. Alternatively, the pair of pumpingelectrodes 312 and 314 may be configured to electrochemically pump aselected gas through layer 301 and into internal cavity 322. Herein,pumping electrodes pair 312 and 314 may be referred to as an O₂ pumpingcell.

Electrodes 312, 314, 316, and 318 may be made of various suitablematerials. In some embodiments, electrodes 312, 314, 316, and 318 may beat least partially made of a material that catalyzes the dissociation ofmolecular oxygen. Examples of such materials include, but are notlimited to, electrodes containing platinum and/or silver.

The process of electrochemically pumping the oxygen out of or intointernal cavity 322 includes applying a voltage V_(p) across pumpingelectrode pair 312 and 314. The pumping voltage V_(p) applied to the O₂pumping cell pumps oxygen into or out of first internal cavity 322 inorder to maintain a stoichiometric level of oxygen in the cavity pumpingcell. The resulting pumping current I_(p) is proportional to theconcentration of oxygen in the exhaust gas. A control system (not shownin FIG. 3) generates the pumping current signal I_(p) as a function ofthe intensity of the applied pumping voltage V_(p) required to maintaina stoichiometric level within the first internal cavity 322. Thus, alean mixture will cause oxygen to be pumped out of internal cavity 322and a rich mixture will cause oxygen to be pumped into internal cavity322. Further, the output gain of the pumping current may be varied viathe variable gain operational amplifier (e.g., op-amp). By varying thereference voltage and the output gain of the op-amp, the oxygen sensormay provide a higher resolution signal.

It should be appreciated that the oxygen sensor described herein ismerely an example embodiment of an oxygen sensor, and that otherembodiments of oxygen sensors may have additional and/or alternativefeatures and/or designs.

Turning now to FIG. 4, an example routine 400 is shown for using anintake oxygen sensor (such as sensor 172 of FIGS. 1-2) for estimatingthe alcohol content and/or composition of an injected wiper fluid basedon a change in pumping current of the intake oxygen sensor. The methodenables the composition of the wiper fluid to be determined accurately,and without the need for additional sensors.

At 402, the method includes estimating and/or measuring engine operatingconditions. These include, for example, engine speed, engine load,boost, ambient conditions (temperature, pressure, humidity), EGR,air-fuel ratio, etc.

At 404, it may be determined if wiper fluid has been recently refilledin the wiper fluid reservoir. In particular, the wiper fluid compositionestimation may be triggered by a recent wiper fluid refill event. Thisallows the composition of the available wiper fluid to be accuratelyknown. Consequently, the wiper fluid may be more reliably used for knockcontrol in addition to wiper washing functions. In alternate examples,the composition may be estimated in response to an operator request forwiper fluid composition estimation. For example, the composition of thewiper fluid may be determined periodically, such as once every thresholddistance of vehicle travel, once every duration of engine operation orvehicle travel, once every threshold number of engine cycles, etc.

Herein, the wiper fluid (also referred to as a windshield washer fluidor just washer fluid) is a water-alcohol blend that includes nogasoline. In other words, the alcohol is the only source of hydrocarbonsin the wiper fluid. In one example, the alcohol in the water-alcoholblend is one or more of ethanol, methanol, propanol, isopropanol, etc.It will be appreciated that while the present routine depicts thecomposition estimation of a wiper fluid to enable the fluid to be alsoleveraged as a knock control fluid, this is not meant to be limiting,and in other examples, the composition of an engine coolant fluid may bedetermined via the use of the intake oxygen sensor to enable the fluidto be also leveraged as a knock control fluid.

If wiper fluid has not been refilled in the reservoir, or if other wiperfluid composition estimation conditions have not been met, then at 424,the method includes continuing to operate the intake oxygen sensor as anoxygen sensor. Further, one or more engine operating parameters areadjusted based on the output of the oxygen sensor. As non-limitingexamples, the output of the intake oxygen sensor may be used for EGRestimation and EGR control, as well as combustion air-fuel ratiocontrol. For example, based on the estimated oxygen concentration of theintake aircharge, an amount of EGR delivered to the engine intake may beadjusted (e.g., to provide a desired engine dilution or a desiredcombustion air-fuel ratio). As another example, based on the estimatedoxygen concentration of the intake aircharge, cylinder fueling may beadjusted.

If wiper fluid has been refilled in the reservoir, or if other wiperfluid composition estimation conditions have been met, then at 406, themethod includes injecting an amount (herein also referred to as theinjection mass) of the wiper fluid into the intake passage, downstreamof the intake throttle (and upstream of the intake valve). In oneexample, the injection mass is set to be an amount that will provide asignificant change in the output of the intake oxygen sensor

At 408, a transfer function may be determined for the wiper fluid basedon the intake manifold airflow level (as determined, for example, basedon the output of a MAF sensor), as well as the wiper fluid injectionmass. The transfer function may represent an expected change in pumpingcurrent of the intake oxygen sensor with injection mass, for a givenreference voltage. This change is then compared to a baseline reading ofthe oxygen concentration when no washer fluid is injected. Similarly,the manifold airflow may be interpreted from a MAP sensor and a look-uptable that determines the air mass flow rate in a speed-density system.At 410, a first pumping voltage (herein also called as the referencevoltage) (V₁) is applied to the oxygen sensor. The first pumping voltagemay be a lower reference voltage that pumps oxygen from the oxygenpumping cell, but may have a low enough value so as to not dissociatewater (e.g., H₂O) molecules in the pumping cell (e.g., V₁=450 mV). Whenthe first voltage is applied to the pumping cell, a first pumpingcurrent (I₁) may be generated. In this example, because wiper fluid isinjected into the engine intake manifold, the first pumping current maybe indicative of an amount of oxygen that either reacted with thesensing element of the oxygen sensor, or was displaced due to thedilution effect of the water.

At 412, the method includes determining the composition of the wiperfluid based on the output of the intake oxygen sensor. In particular,change in the pumping current of the sensor may be monitored followingthe applying of the lower pumping voltage, and a controller may estimatethe composition of the wiper fluid by learning a first portion of thechange in pumping current due to a water content of the fluid, whilelearning a second portion of the change in pumping current due to analcohol content of the blend. In particular, an alcohol content of(e.g., a percentage alcohol in) the wiper fluid is determined based onthe change in sensor pumping current and further based on the fluidinjection mass (as injected at 406). The estimating of an alcoholcontent of the water-alcohol blend includes, at 414, learning a firstportion of the change in pumping current due to a water content of theblend, and at 416, learning a second portion of the change in pumpingcurrent due to an alcohol content of the blend.

In one example, an amount of water in the sample may be determined basedon the first pumping current and the transfer function. The amount ofalcohol may then be identified based on the estimated water content.Because ambient humidity may also contribute to an amount of water inthe intake charge, an ambient humidity estimate (as determined by adedicated humidity sensor or detected by an intake or exhaust gas oxygensensor during selected conditions) may be subtracted from the determinedamount of water. In some embodiments, the computer readable storagemedium of the control system receiving communication from the sensor mayinclude instructions for identifying the amount of alcohol by referringto a graph depicting examples of the relationship between change inoxygen sensor output and injection mass with change in percent alcoholcontent of the wiper fluid (as discussed below with reference to FIG.6), the graph data stored on the computer readable storage medium in theform of a lookup table, for example. Therein, as the amount of alcohol(e.g., ethanol or methanol) in the injected wiper fluid increases, theamount of water estimated by the intake oxygen sensor maycorrespondingly decrease. As shown in FIG. 6, for a given mass of washerfluid injected into the intake air stream, a higher change (delta) inintake oxygen sensor output will reflect a higher methanol-to-waterratio. Consequently, the change in oxygen percentage (delta_O2%) will becloser to the 100% MeOH line, and the engine controller maydetermine/identify the line with constant methanol concentration thatcorresponds to that operating point.

In particular, Applicants have recognized that the effect of the watercomponent of the water-alcohol blend on the intake oxygen sensor pumpingcurrent is distinct from the effect of the alcohol component (includingthe alcohol content and the alcohol type) of the water-alcohol blend onthe intake oxygen sensor pumping current. For example, injecting 1%water (by volume) into intake air results in a 0.2% reduction in oxygenconcentration as measured by the intake oxygen sensor since it has adilution effect on the oxygen concentration. However, injecting 1%methanol (by volume) into intake air results in a 1.5% reduction inoxygen concentration as measured by the intake oxygen sensor due tomethanol combusting with the oxygen at the oxygen sensor's sensingelement as indicated below.

CH₃OH+1.5O₂=CO₂+H₂O

Hence, if a 2% of the washer fluid (water+methanol) mixture is injected,this will result in a total reduction in oxygen of 2.5% (in thisexample), 0.2/1.7 or 11.7% of that reduction is due to water, and aremaining 1.5/1.7 or 88.3% of that reduction is due to methanol.

Thus, learning the first portion may include determining a first valueof methanol-to-water concentration in the blend (based on the change inpumping current). Further, learning the second portion may includedetermining a second value of methanol-to-water concentration in theblend that is learned based on the monitored change in pumping currentand further based on the amount of water-alcohol blend injected. Herein,the second value may be reflective of a base concentration of oxygen inthe ambient air. In addition, the controller may compare the first valueto the second value.

As an example, the controller may reference a look-up table or a map,such as the example map of FIG. 6, to determine the percentage ofalcohol in the knock control fluid. The map may be a 3D map requiring 2inputs, the mass of fluid injected and the change in intake oxygensensor pumping current, to provide an output regarding the percentage ofalcohol in the injected knock control fluid.

Referring to FIG. 6, map 600 depicts one such example map. Inparticular, map 600 depicts change in intake oxygen sensor along they-axis (Delta_O2%) and injection mass of washer fluid(M_washer_fluid_inj) along the y-axis. Herein, the washer fluid is awater-methanol blend that includes no gasoline. The map is calibratedfor 0% methanol (MeOH) and 100% methanol, as well as one or moreintermediate methanol percentages. As can be seen, for a given injectionmass, with increasing methanol content, a larger change in oxygen sensoroutput is observed. In other words, using the map, the methanolpercentage (Methanol_pct) may be estimated as: Methanol_pct=fn(delta_O2, M_washer_fluid_inj). Thus, using a map such as the map ofFIG. 6, a controller may be able to estimate the alcohol (e.g.,methanol) content of the injected wiper fluid.

Returning to FIG. 4, a composition of the water-alcohol blend wiperfluid based on the learned first portion and second portion, and furtherbased on the injection amount. That is, based on the alcohol content ofthe water-alcohol blend wiper fluid, the composition of thewater-alcohol blend may be determined and updated.

At 418, upon learning the composition of the wiper fluid, an octanevalue of the fluid is updated. In addition, a fuel octane estimate forthe engine system may be updated. For example, an octane modifier termusing during feed-forward control of knock may be updated. In oneexample, the updating includes increasing the octane value as thealcohol (ethanol or methanol) content of the wiper fluid increases or asthe water content of the wiper fluid decreases.

At 420, upon confirming the composition of the wiper fluid, the fluidmay be used as a knock control fluid as required. For example, inresponse to an indication of knock, or in anticipation of possibleknock, an amount of the wiper fluid may be injected based on the octanerequirement of the engine (to address the knock) relative to the updatedoctane value of the fluid.

At 422, one or more engine operating parameters are adjusted based onthe updated wiper fluid and fuel octane estimate. For example, a basespark timing applied may be adjusted (e.g., advanced from MBT). Asanother example, borderline spark value may be adjusted (e.g.,advanced). As still another example, one or more of an EGR schedule, VCTschedule, variable compression ratio, dual fuel injection schedule,etc., may be adjusted.

Upon completing the wiper fluid composition estimation via the intakeoxygen sensor, the method may return to 424 wherein the sensor mayresume being operated for oxygen sensing for the purposes of EGRcontrol, air-fuel ratio control, and the like.

In this way, wiper fluid composition estimation can be improved,allowing the use of the fluid to be expanded to other functions. Forexample, the composition estimation may allow for improved usage ofwiper fluid outside of windshield wiping, or of engine coolant outsideof engine cooling. In particular, the wiper fluid and/or the enginecoolant may be used more reliably and consistently as a knock controlfluid for addressing knock. By improving the usage of a water-alcoholblend in the mitigation of knock, octane requirements of fuel can bereduced, while knock is addressed, allowing more power to be gained fromthe engine. In addition, by reducing the need for spark retard, fueleconomy benefits are achieved.

Turning now to FIG. 5, an example routine 500 is shown for using anexhaust oxygen sensor (such as sensor 225 of FIGS. 1-2) for estimatingthe alcohol content and/or composition of an injected wiper fluid basedon a change in pumping current of the exhaust oxygen sensor. The methodenables the composition of the wiper fluid to be determined accurately,and without the need for additional sensors.

At 502, the method includes estimating and/or measuring engine operatingconditions. These include, for example, engine speed, engine load,boost, ambient conditions (temperature, pressure, humidity), EGR,air-fuel ratio, etc.

At 504, it may be determined if wiper fluid has been recently refilledin the wiper fluid reservoir. In particular, the wiper fluid compositionestimation may be triggered by a recent wiper fluid refill event. Thisallows the composition of the available wiper fluid to be accuratelyknown. Consequently, the wiper fluid may be more reliably used for knockcontrol in addition to wiper washing functions. In alternate examples,the composition may be estimated in response to an operator request forwiper fluid composition estimation. For example, the composition of thewiper fluid may be determined periodically, such as once every thresholddistance of vehicle travel, once every duration of engine operation orvehicle travel, once every threshold number of engine cycles, etc.

Herein, the wiper fluid (also referred to as a windshield washer fluidor just washer fluid) is a water-alcohol blend that includes nogasoline. In other words, the alcohol is the only source of hydrocarbonsin the wiper fluid. In one example, the alcohol in the water-alcoholblend is one or more of ethanol, methanol, propanol, isopropanol, etc.It will be appreciated that while the present routine depicts thecomposition estimation of a wiper fluid to enable the fluid to be alsoleveraged as a knock control fluid, this is not meant to be limiting,and in other examples, the composition of an engine coolant fluid may bedetermined via the use of the intake oxygen sensor to enable the fluidto be also leveraged as a knock control fluid.

If wiper fluid has not been refilled in the reservoir, or if other wiperfluid composition estimation conditions have not been met, then at 540,it may be determined if fueling conditions are present. Fuelingconditions include vehicle acceleration conditions and engine operatingconditions in which the fuel supply is uninterrupted and the enginecontinues spinning with at least one intake valve and one exhaust valveoperating; and with air flowing through one or more of the cylinders.Under fueling conditions, combustion is carried out in the combustionchamber and ambient air may move through the cylinder from the intake tothe exhaust.

In comparison, non-fueling conditions include vehicle decelerationconditions and engine operating conditions in which the fuel supply isinterrupted but the engine continues spinning and at least one intakevalve and one exhaust valve are operating; thus, air is flowing throughone or more of the cylinders, but fuel is not injected in the cylinders.Under non-fueling conditions, combustion is not carried out but ambientair may move through the cylinder from the intake to the exhaust.

If fueling conditions are confirmed, at 542, the method includesdetermining if feedback air-fuel ratio control based on the sensor, oralcohol detection by the sensor, is desired or to be carried out. Theselection may be based on operating conditions, such as a duration sincea last determination of alcohol, or whether closed loop air-fuel ratiocontrol is enabled. For example, if feedback air-fuel ratio control isdisabled, the routine may continue to determine alcohol content, whereasif feedback air-fuel ratio is commanded or enabled, the routine maycontinue to perform such feedback air-fuel ratio control (withoutdetermining alcohol content). If it is determined that feedback controlis desired, or if fueling conditions are not confirmed at 540, themethod moves to 550 and the sensor is operated as an exhaust oxygen(e.g., O₂) sensor to determine an oxygen concentration and/or air-fuelratio of the exhaust gas. Further, one or more engine operatingparameters are adjusted based on the output of the oxygen sensor. Asnon-limiting examples, the output of the exhaust oxygen sensor may beused for EGR estimation and EGR control, as well as combustion air-fuelratio control. Then the routine ends.

If alcohol detection is desired, the method proceeds to 544 where it isfirst confirmed that the exhaust gas recirculation (EGR) valve isalready closed (else the valve is actively closed). This ensures thatthe amount of EGR entering the combustion chamber is substantially zero.Next, the method includes modulating a reference voltage applied to theexhaust gas sensor. Specifically, a first pumping voltage (V₁) and asecond pumping voltage (V₂) are sequentially applied to the exhaust gassensor. The first pumping voltage may pump oxygen from the oxygenpumping cell, but may have a low enough valve so as to not dissociatewater (e.g., H₂O) molecules in the pumping cell (e.g., V₁=450 mV). Insome examples, the first pumping voltage applied to the sensor at 544may be the same as the first pumping voltage applied to the sensor at410 of FIG. 4. When the first voltage is applied to the pumping cell, afirst pumping current (I₁) may be generated. In this example, becausefuel is injected to the engine and combustion is carried out, the firstpumping current may be indicative of an amount of oxygen in the exhaustgas.

The second pumping voltage (V₂) applied to the pumping cell of theexhaust gas sensor. may be greater than the first pumping voltage, andthe second voltage may be high enough to dissociate oxygen compoundssuch as water molecules. Application of the second pumping voltageacross the oxygen pumping cell may generate a second pumping current(I₂). The second pumping current may be indicative of an amount ofoxygen and water in the sample gas (e.g., oxygen that already exists inthe sample gas plus oxygen from water molecules dissociated when thesecond pumping voltage is applied).

Once the first and second pumping currents are generated, an alcoholcontent of the fuel may be determined based on an amount of water in thesample gas at 546. For example, the first pumping current may besubtracted from the second pumping current to determine a value thatcorresponds to an amount of water. Then, the amount of alcohol in thefuel may be identified. For example, the amount of water in the exhaustgas may be proportional to an amount of alcohol (e.g., a percent ofethanol) in the fuel injected to the engine. Because ambient humiditymay also contribute to an amount of water in the exhaust gas, an ambienthumidity estimate may be subtracted from the determined amount of water.In some embodiments, the computer readable storage medium of the controlsystem receiving communication from the sensor may include instructionsfor identifying the amount of alcohol based on a look-up table that usesthe change in pumping current as an input.

Upon learning the fuel alcohol content of the injected fuel, at 548, afuel octane estimate is updated. For example, an octane modifier termusing during feed-forward control of knock may be updated. In oneexample, the updating includes increasing the fuel octane estimate asthe alcohol content of the injected fuel increases. Further, one or moreengine operating parameters are adjusted based on the updated fueloctane estimate. For example, a base spark timing applied may beadjusted (e.g., advanced from MBT). As another example, borderline sparkvalue may be adjusted (e.g., advanced) As still another example, an EGRschedule of the engine may be adjusted.

Returning to 504, if the wiper fluid is refilled, or if other wiperfluid composition estimation conditions have been met, then at 506, themethod includes injecting an amount (herein also referred to as theinjection mass) of the wiper fluid into the engine. In one example, thewiper/washer fluid may be injected into the intake passage, downstreamof the intake throttle (and upstream of the exhaust valve). In anotherexample, an engine fuel injector may inject the wiper/washer fluiddirectly inside the cylinder. Herein, since the washer fluid compositionis to be detected using exhaust gas, the fluid can be injected andcombusted in the cylinder. In one example, the injection mass of thewiper fluid injection is set to be an amount that will provide asignificant change in the output of the exhaust oxygen sensor.

At 508, a transfer function may be determined for the wiper fluid basedon the intake manifold airflow level (as determined, for example, basedon the output of a MAF sensor), as well as the wiper fluid injectionmass. The transfer function may represent an expected change in pumpingcurrent of the exhaust oxygen sensor with injection mass, for a givenreference voltage. Similarly, the manifold airflow may be interpretedfrom a MAP sensor and a look-up table that determines the air mass flowrate in a speed-density system

While the engine is being fueled and cylinder are combusting, at 510,the method includes determining if the amount of positive crankcaseventilation (PCV) is at a desired level. Herein, the desired level mayinclude PCV being lower than a threshold amount. In one example, it maybe desired that there be substantially no PCV flow. As an example, ifthe engine is operating in a higher speed range, there may be increasedPCV flow from the engine crankcase into the intake manifold. Otherexample conditions where PCV flow is elevated include increased manifoldvacuum conditions, increased crankcase pressure conditions, high ambienttemperature conditions, combinations thereof, etc. As such, wiper fluidalcohol content estimation may be enabled only during conditions whenPCV flow is lower than a threshold level (e.g., when PCV is disabled) toreduce interference from PCV hydrocarbons.

If the PCV flow is above the desired level (e.g., the PCV flow is high),the method returns to 550 wherein the sensor is operated as an exhaustoxygen sensor to determine an oxygen concentration of the intake air forair-fuel control, for example, and the routine ends.

On the other hand, if PCV is at a desired level (e.g., the PCV flow islow), the method continues to 512 where it is determined if the exhaustgas recirculation (EGR) valve is closed. If it is determined that theEGR valve is open, the method moves to 514 and the EGR valve is closed.As such, wiper fluid alcohol content estimation may be enabled onlyduring conditions when EGR flow is lower than a threshold level (e.g.,when EGR is disabled) to reduce interference from EGR hydrocarbons.

Once the EGR valve is closed or if it is determined that the EGR valveis closed at 512, and thus the amount of EGR entering the combustionchamber is substantially zero, the method proceeds to 516 where it isdetermined if the fuel vapor purge valve is closed. If it is determinedthat the fuel vapor purge valve is open, the method moves to 518 and thefuel vapor purge valve is closed. Fuel vapor that is stored in the fuelvapor canister may also have an alcohol content and may corrupt theresults of a wiper fluid composition estimation. In particular, fuelvapor entering the combustion chamber may affect the amount of alcoholdetected by the exhaust oxygen sensor resulting in an inaccurateestimate. Thus, wiper fluid composition estimation may be enabled onlyduring conditions when purge flow is lower than a threshold level (e.g.,when canister purge is disabled). By recording the response of theexhaust oxygen sensor to injection of a knock control fluid in theabsence of EGR, PCV, or purge, a more accurate estimate of the air-fuelratio of the water-alcohol blend being injected is achieved. As such,this provides an improvement in the fuel economy and performance of theengine system.

Once the fuel vapor purge valve is closed at 518 or if is determinedthat the fuel vapor purge valve is closed at 516, the method continuesto 520 wherein the method includes modulating a reference voltage of theexhaust oxygen sensor. The modulating includes alternating the referencevoltage of the oxygen sensor between a first voltage and a secondvoltage, the first and second voltages applied successively. Inparticular, a first pumping voltage (V₁) may be initially applied to theexhaust oxygen sensor. The first pumping voltage may pump oxygen fromthe oxygen pumping cell, but may have a low enough value so as to notdissociate water (e.g., H₂O) molecules in the pumping cell (e.g., V₁=450mV). In some examples, the first pumping voltage applied to the sensorfor estimating the alcohol content of the wiper fluid may be the same asthe first pumping voltage applied to the sensor for estimating thealcohol content of the injected fuel (as detailed at 544). When thefirst voltage is applied to the pumping cell, a first pumping current(I₁) may be generated. In this example, the first pumping current may beindicative of an amount of oxygen in the aircharge.

The modulating then includes applying a second pumping voltage (V₂) tothe pumping cell of the exhaust oxygen sensor. The second pumpingvoltage may be greater than the first pumping voltage, and the secondvoltage may be high enough to dissociate oxygen compounds such as watermolecules (e.g., V₂=950 or 1050 mV). Application of the second pumpingvoltage across the oxygen pumping cell may generate a second pumpingcurrent (I₂). The second pumping current may be indicative of an amountof oxygen and water in the sample gas (e.g., oxygen that already existsin the sample gas plus oxygen from water molecules dissociated when thesecond pumping voltage is applied).

After the first and second pumping currents are generated, a change inthe pumping current of the sensor is monitored. At 522, an alcoholcontent of (e.g., a percentage alcohol in) the wiper fluid is determinedbased on the change in sensor pumping current and further based on thefluid injection mass (as injected at 506). The estimating of an alcoholcontent of the water-alcohol blend includes, at 524, learning a firstportion of the change in pumping current due to a water content of theblend, and at 526, learning a second portion of the change in pumpingcurrent due to an alcohol content of the blend.

In one example, an amount of water in the sample may be determined bysubtracting the first pumping current from the second pumping current.The amount of alcohol in the wiper fluid may then be identified based onthe estimated water content. For example, the amount of water in thefluid may be proportional to an amount of alcohol (e.g., a percent ofethanol or methanol) in the injected water-alcohol blend. Becauseambient humidity may also contribute to an amount of water in the intakecharge, an ambient humidity estimate (as determined by a dedicatedhumidity sensor or detected by an exhaust gas oxygen sensor, or theintake oxygen sensor during other selected conditions) may be subtractedfrom the determined amount of water. In some embodiments, the computerreadable storage medium of the control system receiving communicationfrom the sensor may include instructions for identifying the amount ofalcohol by referring to a graph depicting examples of the relationshipbetween change in oxygen sensor output and injection mass water withchange in percent alcohol content of a knock control fluid (as discussedabove with reference to FIG. 6), the graph data stored on the computerreadable storage medium in the form of a lookup table, for example.Therein, as the amount of alcohol (e.g., ethanol or methanol) in theinjected wiper fluid increases, the amount of water estimated by theintake oxygen sensor may correspondingly decrease. As shown in FIG. 6,for a given mass of washer fluid injected into the intake air stream orengine cylinder, a higher change (delta) in Oxygen sensor output willreflect a higher methanol-to-water ratio; in this case the delta_O2%will be closer to the 100% MeOH line, and the engine controller maydetermine the line with constant methanol concentration that correspondsto that operating point. In particular, Applicants have recognized thatthe effect of the water component of the water-alcohol blend on theexhaust oxygen sensor pumping current is distinct from the effect of thealcohol component (including the alcohol content and the alcohol type)of the water-alcohol blend on the exhaust oxygen sensor pumping current.For example, injecting 1% water (by volume) into intake air results in a0.2% reduction in oxygen concentration as measured by the exhaust oxygensensor since it has a dilution effect on the oxygen concentration.However, injecting 1% methanol (by volume) into intake air results in a1.5% reduction in oxygen concentration as measured by the exhaust oxygensensor due to methanol combusting with the oxygen at the oxygen sensor'ssensing element as indicated below.

CH₃OH+1.5O₂=CO₂+H₂O

Hence, if 2% of the wiper fluid (water+methanol) mixture is injected,this will result in a total reduction in oxygen of 2.5% (in thisexample), 0.2/1.7 or 11.7% of that reduction is due to water, and aremaining 1.5/1.7 or 88.3% of that reduction is due to methanol.

Thus, learning the first portion may include determining a first valueof methanol-to-water concentration in the blend (based on the change inpumping current). Further, learning the second portion may includedetermining a second value of methanol-to-water concentration in theblend that is learned based on the monitored change in pumping currentand further based on the amount of water-alcohol blend injected. Herein,the second value may be reflective of a base concentration of oxygen inthe ambient air. In addition, the controller may compare the first valueto the second value.

As an example, the controller may reference a look-up table or a map,such as the example map of FIG. 6, to determine the percentage ofalcohol in the knock control fluid. As discussed earlier, the map may bea 3D map requiring 2 inputs, the mass of fluid injected and the changein exhaust oxygen sensor pumping current, to provide an output regardingthe percentage of alcohol in the injected wiper fluid.

It will be appreciated that in alternate examples, the wiper fluidestimation may be performed using the exhaust gas oxygen sensor duringan engine non-fueling condition where at least one intake valve and oneexhaust valve are operating. For example, the modulating may beperformed during a deceleration fuel shut-off (DFSO) event.

At 528, upon learning the composition of the wiper fluid, an octanevalue of the fluid is updated. In addition, a fuel octane estimate forthe engine system may be updated. For example, an octane modifier termusing during feed-forward control of knock may be updated. In oneexample, the updating includes increasing the octane value as thealcohol (ethanol or methanol) content of the wiper fluid increases or asthe water content of the wiper fluid decreases.

At 530, upon confirming the composition of the wiper fluid, the fluidmay be used as a knock control fluid as required. For example, inresponse to an indication of knock, or in anticipation of possibleknock, an amount of the wiper fluid may be injected based on the octanerequirement of the engine (to address the knock) relative to the updatedoctane value of the fluid.

At 532, one or more engine operating parameters are adjusted based onthe updated wiper fluid and fuel octane estimate. For example, a basespark timing applied may be adjusted (e.g., advanced from MBT). Asanother example, borderline spark value may be adjusted (e.g.,advanced/). As still another example, one or more of an EGR schedule ofthe engine, VCT schedule, variable compression ratio, dual fuelinjection schedule, etc., may be adjusted.

Upon completing the wiper fluid composition estimation via the exhaustoxygen sensor, the method may return to 550 wherein the sensor mayresume being operated for oxygen sensing for the purposes of EGRcontrol, air-fuel ratio control, and the like.

In this way, the composition of a wiper fluid as well as an injectedfuel can be determined using an exhaust oxygen sensor. For example,during a first condition, a water-alcohol blend may be injected into anengine cylinder and an alcohol composition of the water-alcohol blendmay be determined based on a change in pumping current of the exhaustoxygen sensor. Then, during a second condition, a gasoline-alcohol blendmay be injected into an engine cylinder and an alcohol composition ofthe gasoline-alcohol blend may be determined based on a change inpumping current of the exhaust oxygen sensor. By accurately and reliablylearning the alcohol content and composition of a wiper fluid, the useof the fluid can be expanded for knock control, improving the robustnessof the engine system. By using the same oxygen sensor to estimate thealcohol content of the knock control fluid and the alcohol content ofthe injected fuel, the need for a dedicated sensor for determining thecomposition of the knock control fluid is reduced.

One example engine method comprises: injecting an amount of awater-alcohol blend; applying a reference voltage to an intake oxygensensor; monitoring a change in pumping current of the sensor; learning afirst portion of the change in pumping current due to a water content ofthe blend; and learning a second portion of the change in pumpingcurrent due to an alcohol content of the blend. The preceding examplemay additionally or optionally further comprise learning a compositionof the blend based on the learned first portion and second portion, andfurther based on the injection amount. Any or all of the precedingexamples may additionally or optionally further comprise adjusting anengine operating parameter based on the learned composition, the engineoperating parameter including one or more of a fuel octane estimate anda fuel injection amount. In any or all of the preceding examples, theblend may additionally or optionally further include no gasoline andwherein the alcohol includes one or more of ethanol and methanol. In anyor all of the preceding examples, the applying may additionally oroptionally further include applying a first lower voltage that does notdissociate water molecules. In any or all of the preceding examples,learning the first portion additionally or optionally further includeslearning a first value of water-to-methanol composition in the blend,based on the change in pumping current. In any or all of the precedingexamples, learning the second portion additionally or optionally furtherincludes determining a second value of methanol-to-water concentrationin the blend that is learned based on the monitored change in pumpingcurrent and further based on the amount of water-alcohol blend injected,and comparing the first value to the second value. Herein, the secondvalue may be reflective of a base concentration of oxygen in the ambientair. In any or all of the preceding examples, the method is additionallyor optionally performed when selected conditions are satisfied, theselected conditions additionally or optionally include followingrefilling of the water-alcohol blend in a reservoir. In any or all ofthe preceding examples, the water-alcohol blend additionally oroptionally includes one of wiper fluid and engine coolant.

Another example method for an engine comprises: during a firstcondition, injecting a water-alcohol blend into an engine cylinder, andlearning an alcohol composition of the water-alcohol blend based on achange in pumping current of an intake oxygen sensor; and during asecond condition, injecting a gasoline-alcohol blend into the enginecylinder, and learning the alcohol composition of the gasoline-alcoholblend based on the change in pumping current of the intake oxygensensor. In the preceding example, the first condition additionally oroptionally includes engine operation following refilling of thewater-alcohol blend in a washer fluid tank of the engine, and the secondcondition additionally or optionally includes engine operation followingrefilling of the gasoline-alcohol blend in a fuel tank of the engine. Inany or all of the preceding examples, additionally or optionally, duringthe second condition, a reference voltage of the intake oxygen sensor ismodulated between a first and a second voltage, and the change inpumping current is responsive to the modulation. Additionally oroptionally, in any or all of the preceding examples, during the secondcondition, only the first reference voltage is applied to the intakeoxygen sensor, and the change in pumping current is responsive to theapplying. In any or all of the preceding examples, during the firstcondition, the alcohol composition of the water-alcohol blend isadditionally or optionally further based on an injection mass. In any orall of the preceding examples, during the first condition, learning analcohol composition of the water-alcohol blend additionally oroptionally includes distinguishing a first portion of the change inpumping current due to a water content of the water-alcohol blend from asecond portion of the change in pumping current due to an alcoholcontent of the water-alcohol blend. In any or all of the precedingexamples, the water-alcohol blend additionally or optionally includes afirst alcohol in a first ratio relative to water, and thegasoline-alcohol blend includes a second alcohol in a second ratiorelative to gasoline, the first alcohol different from the secondalcohol, the first ratio different from the second ratio. Any or all ofthe preceding examples may additionally or optionally further comprise,during the first condition, adjusting a knock-mitigating spark retardamount based on the learned alcohol composition of the water-alcoholblend, and during the second condition, adjusting a feedback air-fuelratio control gains based on the learned alcohol composition of thegasoline-alcohol blend.

Another example engine system comprises an engine including an intakemanifold; a first injector for injecting fuel into an engine cylinder; asecond injector for injecting a knock control fluid into the intakemanifold, downstream of an intake throttle; an EGR system including apassage for recirculating exhaust residuals from downstream of theturbine to upstream of the compressor via an EGR valve; an oxygen sensorcoupled to the intake manifold, downstream of the intake throttle anddownstream of the EGR valve; and a controller. The controller may beconfigured with computer readable instructions stored on non-transitorymemory for: injecting an amount of knock control fluid into thecylinder; applying a lower reference voltage to the oxygen sensor;measuring a change in pumping current of the oxygen sensor; andestimating a composition of the knock control fluid based on theinjection amount and the measured change in pumping current. In thepreceding example, the knock control fluid additionally or optionallyincludes water and alcohol and no fuel, and the controller estimates thecomposition by calculating a first portion of the change in pumpingcurrent due to a water content of the knock control fluid andcalculating a second portion of the change in pumping current due to analcohol content of the knock control fluid. In any or all of thepreceding examples, the controller additionally or optionally includesfurther instructions for updating a fuel octane estimate based on theestimated composition of the knock control fluid. In any or all of thepreceding examples, the controller additionally or optionally includesfurther instructions for: adjusting each of a spark timing and aborderline spark value applied responsive to knock based on the updatedfuel octane estimate, the adjusting including retarding spark timingfrom a base spark timing, and advancing borderline spark towards MBT asthe fuel octane estimate increases.

In this way, based on sensor outputs (e.g., pumping currents) generatedresponsive to voltages applied to the oxygen pumping cell of an enginesystem oxygen sensor during selected conditions, a composition of awater-alcohol blend knock control fluid may be determined accurately andreliably. In particular, a change in the sensor output may be correlatedwith the amount of alcohol in a wiper fluid or engine coolant. In thismanner, an accurate indication of the amount of alcohol (e.g., percentethanol or percent methanol) in the fluid may be identified, allowingthe fluid to be used additionally for knock control. Further, once thecomposition type is determined, various engine operating parameters maybe adjusted to maintain engine and/or emissions efficiency, and improveknock controlling spark usage. The technical effect of improving theestimation of a composition of an injected knock control fluid is thatthe use of the knock control fluid may be expanded.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. An engine method, comprising: injecting an amount of a water-alcoholblend; applying a reference voltage to an intake oxygen sensor;monitoring a change in pumping current of the sensor; learning a firstportion of the change in pumping current due to a water content of theblend; and learning a second portion of the change in pumping currentdue to an alcohol content of the blend.
 2. The method of claim 1,further comprising, learning a composition of the blend based on thelearned first portion and second portion, and further based on theinjection amount.
 3. The method of claim 2, further comprising,adjusting an engine operating parameter based on the learnedcomposition, the engine operating parameter including one or more of afuel octane estimate and a fuel injection amount.
 4. The method of claim1, wherein the blend includes no gasoline and wherein the alcoholincludes one or more of ethanol and methanol.
 5. The method of claim 1,wherein the applying includes applying a first lower voltage that doesnot dissociate water molecules.
 6. The method of claim 1, whereinlearning the first portion includes determining a first value ofmethanol-to-water concentration in the blend.
 7. The method of claim 6,wherein learning the second portion includes: determining a secondmethanol-to-water concentration in the blend that is learned based onthe monitored change in pumping current and further based on the amountof water-alcohol blend injected, the second value reflecting a baseconcentration of oxygen in the ambient air; and comparing the firstvalue to the second value.
 8. The method of claim 1, wherein the methodis performed responsive to selected conditions being identified, theselected conditions include following refilling of the water-alcoholblend in a reservoir.
 9. The method of claim 1, wherein thewater-alcohol blend includes one of wiper fluid and engine coolant. 10.A method for an engine, comprising: during a first condition, injectinga water-alcohol blend into an engine cylinder, and learning an alcoholcomposition of the water-alcohol blend based on a change in pumpingcurrent of an intake oxygen sensor; and during a second condition,injecting a gasoline-alcohol blend into the engine cylinder, andlearning the alcohol composition of the gasoline-alcohol blend based onthe change in pumping current of the intake oxygen sensor.
 11. Themethod of claim 10, wherein the first condition includes engineoperation following refilling of the water-alcohol blend in a washerfluid tank, and wherein the second condition includes engine operationfollowing refilling of the gasoline-alcohol blend in a fuel tank. 12.The method of claim 10, wherein during the second condition, a referencevoltage of the intake oxygen sensor is modulated between a first and asecond voltage, and the change in pumping current is responsive to themodulation, and wherein during the second condition, only the firstreference voltage is applied to the intake oxygen sensor, and the changein pumping current is responsive to the applying.
 13. The method ofclaim 12, wherein during the first condition, the alcohol composition ofthe water-alcohol blend is further based on an injection mass.
 14. Themethod of claim 10, wherein during the first condition, learning analcohol composition of the water-alcohol blend includes distinguishing afirst portion of the change in pumping current due to a water content ofthe water-alcohol blend from a second portion of the change in pumpingcurrent due to an alcohol content of the water-alcohol blend.
 15. Themethod of claim 10, wherein the water-alcohol blend includes a firstalcohol in a first ratio relative to water, and wherein thegasoline-alcohol blend includes a second alcohol in a second ratiorelative to gasoline, the first alcohol different from the secondalcohol, the first ratio different from the second ratio.
 16. The methodof claim 10, further comprising, during the first condition, adjusting aknock-mitigating spark retard amount based on the learned alcoholcomposition of the water-alcohol blend, and during the second condition,adjusting a feedback air-fuel ratio control gains based on the learnedalcohol composition of the gasoline-alcohol blend.
 17. An engine system,comprising: an engine including an intake manifold; a first injector forinjecting fuel into an engine cylinder; a second injector for injectinga knock control fluid into the intake manifold, downstream of an intakethrottle; an EGR system including a passage for recirculating exhaustresiduals from downstream of the turbine to upstream of the compressorvia an EGR valve; an oxygen sensor coupled to the intake manifold,downstream of the intake throttle and downstream of the EGR valve; and acontroller with computer readable instructions stored on non-transitorymemory for: injecting an amount of knock control fluid into thecylinder; applying a lower reference voltage to the oxygen sensor;measuring a change in pumping current of the oxygen sensor; andestimating a composition of the knock control fluid based on theinjection amount and the measured change in pumping current.
 18. Thesystem of claim 17, wherein the knock control fluid includes water andalcohol and no fuel, and wherein the controller estimates thecomposition by calculating a first portion of the change in pumpingcurrent due to a water content of the knock control fluid andcalculating a second portion of the change in pumping current due to analcohol content of the knock control fluid.
 19. The system of claim 17,wherein the controller includes further instructions for: updating afuel octane estimate based on the estimated composition of the knockcontrol fluid.
 20. The system of claim 19, wherein the controllerincludes further instructions for: adjusting each of a spark timing anda borderline spark value applied responsive to knock based on theupdated fuel octane estimate, the adjusting including retarding sparktiming from a base spark timing, and advancing borderline spark towardsMBT as the fuel octane estimate increases.